Two sources of biphoton fields divided by a gap filled with an arbitrary
media allow to measure dispersive properties of the media inside gap in a
wide spectral region. The origin of the method is a modification of the
angle-frequency line shape of spontaneous parametric scattering due to
interference of biphoton fields modified by absorption and dispersion in
gap. This scheme can be described as a non-linear Mach-Zender interferometer.